Sorry Jesse,

 I don't think my original post was very clear. I have gone in a slightly different direction. Same basic idea, but using Templates inside a user control.

I am looking for something like this

http://wss3.theseders.com/robsederblog/Lists/Posts/Post.aspx?List=4c9e886c%2D4b5c%2D4a3e%2D95a0%2De30b3f4a1e9c&ID=67

But I am getting an error on this that says "Type 'System.Web.UserControl' does not have a public property named 'ContentTemplate'

However I do have :)

 [In the User Control]

     private ITemplate _windowContent;

    protected override void OnInit(EventArgs e)
    {

        base.OnInit(e);

        if (_windowContent != null)
        {

            _windowContent.InstantiateIn(webWindowContent);

        }

    }

[PersistenceMode(PersistenceMode.InnerProperty),
    TemplateContainer(typeof(TemplateControl))]
    public ITemplate ContentTemplate
    {

        get { return _windowContent; }

        set { _windowContent = value; }

    }